1. Field of the Invention
The present invention relates to a process for the low level desulphurization of hydrocarbons containing sulfides, disulfides, trisulfides or tetrasulfides or mixtures thereof.
2. Description of the Background
It is generally known that sulfur compounds act as catalyst poisons, in particular for catalysts containing transition metals of group VIII. Because of their frequently unpleasant odors, and because they are frequently found in hydrocarbons such as in propane and butanes which are used to an increasing extent in aerosol technology, the removal of such sulfur compounds from such materials is desired. In this context even sulfur contents far below 0.1 ppm may still give an unpleasant odor.
The removal of di-, tri- and higher oligosulfides is particularly important, because many petrochemically recovered hydrocarbons contain such compound(s) as a result of their preliminary purification, for instance, the processing of hydrocarbons by the Merox process as described in EP-A 0 235 462.
It is known that sulfides and disulfides can be removed from substances by adsorption. Adsorbents which have been used frequently for this purpose include activated charcoal, zeolites and porous silicates. N. Gryazev et al describe the adsorption of sulfides and disulfides from solutions on zeolites, silica gel and aluminum silicates (Khim. Seraorg. Soedin. Soderzh. Neft. Nefteprod., 9 (1972), 415-420). S. Tanada and K. Boki similarly investigated the removal of sulfur compounds on zeolites and silicates and in addition also studied the adsorption of dimethylsulfide on activated charcoal (Tokushima Bunri Daigaku Kenkyo Kiyo, 15 (1976), 33-38).
I. P. Muklenov et al. have shown that dimethyl sulfide and dimethyl disulfide in addition to other compounds can be removed from waste gases by adsorption on activated charcoal (Bum. Prom.-st. 7 (1978), 27-28). Further, N. A. Sankhin et al., Bum. Prom-st. 11 (1979), 27-28, have shown the adsorption of dimethyl sulfide and dimethyl disulfide and in addition other sulfur compounds on activated charcoal, which compounds are produced during the manufacture of sulfates.
T. Suetaka and M. Munemori have also described the adsorption of sulfides, more particularly the adsorption of dimethyl sulfide and diethyl sulfide, on activated charcoal [Akushu no Kenkyn 18, 72 (1987), 32 -34.
Shcherbina et al. in Obshch. Prikl. Khim., No. 5 (1972), 113-114, have described the adsorption of sulfur compounds on sodium zeolites of the X-type, while Mikhal'skaya et al., Khim. Tekhol. 9 (1975), 64 -66 have shown the adsorption of sulfur compounds on sodium zeolites of the Y type. Disulfides as well as mercaptans can be removed from hydrocarbons by means of sodium zeolites of the X type, whereas with sulfides this is stated to take place only incompletely.
JP-OS 59/160 584 describes the adsorption of disulfides and sulfides in addition to H.sub.2 S, COS and mercaptans on activated charcoal containing heavy metals.
In addition it is known from DD-PS 241 196 and DD-PS 241 197 that hydrogen sulfide and organic sulfur compounds can be removed from carbon dioxide-containing gas mixtures by adsorption on zinc and manganese zeolites of the X type. Using this type of adsorbent DD-PS 241 196 discloses a process for preventing the formation of carbon oxysulfide in desulfurization processes and DD-PS 241 197 in sorptive separation processes. The objective in these processes is to reduce the loss of sulfur as a result of carbon oxysulfide formation having regard to the downstream production of elemental sulfur. However, both processes can be carried out only in the very limited temperature range of 10.degree. to 50.degree. C. Further, DD-PS 241 197 shows that it is possible to thermally regenerate zeolites loaded with sulfur compounds.
None of the processes shown to date for the adsorption of sulfides and disulfides are suitable for the low level desulfurization of hydrocarbons. A need therefore continues to exist for a method of effectively desulfurizing hydrocarbons.